It's "best tools" week! For the third straight year, Keith Law lays out his rankings (and reasoning) for the players with the best tools in baseball. Tuesday he evaluates the top pitches across six different pitch types (see last year's rankings here). Monday he ranked the best hitting tools; Wednesday will be the top fielding/throwing tools.
4. Joe Kelly, Boston Red Sox
Of course, the hardest throwers are all relievers -- FanGraphs' velocity data shows the top 12 pitchers, by average fastball velocity, work out of the pen, with Cincinnati's Luis Castillo the hardest-throwing starter at 97.5 mph -- so this list ends up a mashup of the relievers with the biggest velo and the starters with the most effective fastballs.